cli: rewrite help text for AI-driven discovery

Frontier models tend to discover a CLI by running --help, scanning
the Long description, and inferring the dominant workflow from the
examples. Today's banger help reads like a man page index — every
verb has a one-line Short and nothing else. This rewrites the
groups (banger, vm, vm workspace, image, kernel, system,
ssh-config) so each landing page answers "what is this for, what's
the 80% command, what comes next" in three to ten lines, with
runnable examples.

Also disambiguates the near-twin lifecycle commands so a model
reading the subcommand index can tell stop/kill/delete apart at a
glance:

  start    Start a stopped VM
  stop     Stop a running VM gracefully
  restart  Stop then start a VM
  kill     Force-kill a VM (use when 'vm stop' hangs)
  delete   Stop a VM and remove its disks (irreversible)

vm create / vm ssh / vm logs / vm show pick up Long descriptions
and examples for the same reason. No behaviour changes; help text
only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/cli/banger.go

@@ -21,8 +21,31 @@ func NewBangerCommand() *cobra.Command {
 
 func (d *deps) newRootCommand() *cobra.Command {
 	root := &cobra.Command{
-		Use:           "banger",
-		Short:         "Manage development VMs and images",
+		Use:   "banger",
+		Short: "Run development sandboxes as Firecracker microVMs",
+		Long: strings.TrimSpace(`
+banger runs disposable development sandboxes as Firecracker microVMs.
+Each sandbox boots in a few seconds, gets its own root filesystem and
+network, and exits on demand.
+
+The most common workflow is one command:
+
+  banger vm run                          bare sandbox, drops into ssh
+  banger vm run ./repo                   ships a repo into /root/repo, drops into ssh
+  banger vm run ./repo -- make test      ships a repo, runs the command, exits with its status
+
+For a longer-lived VM, use 'banger vm create' to provision and
+'banger vm ssh <name>' to attach. 'banger ps' lists running VMs;
+'banger vm list --all' shows stopped ones too.
+
+First-time setup, in order:
+  sudo banger system install             install the systemd services
+  banger doctor                          confirm the host is ready
+  banger image pull debian-bookworm      fetch a default image
+
+Run 'banger <command> --help' for any subcommand. Run 'banger doctor'
+to diagnose host readiness problems.
+`),
 		SilenceUsage:  true,
 		SilenceErrors: true,
 		RunE:          helpNoArgs,
@@ -46,7 +69,21 @@ func (d *deps) newDoctorCommand() *cobra.Command {
 	return &cobra.Command{
 		Use:   "doctor",
 		Short: "Check host and runtime readiness",
-		Args:  noArgsUsage("usage: banger doctor"),
+		Long: strings.TrimSpace(`
+Check that the host has everything banger needs to boot guests:
+required tools (mkfs.ext4, debugfs, dmsetup, ip, iptables, ...), KVM
+access, daemon reachability, and per-feature preflight (NAT, DNS
+routing, work-disk seeding).
+
+Run 'banger doctor':
+  - after 'banger system install' to confirm the install took
+  - after upgrading the host kernel or banger itself
+  - when 'banger vm run' fails with an unclear error
+
+Exit code is non-zero if any check fails. Warnings are reported but
+do not fail the run.
+`),
+		Args: noArgsUsage("usage: banger doctor"),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			report, err := d.doctor(cmd.Context())
 			if err != nil {